HONG KONG (Reuters) - Hong Kong voted on Sunday in its first major election since pro-democracy protests in 2014 and one of its most contentious, with a push for independence among disaffected younger candidates and voters stoking tension with China's government.

The vote is for a 70-seat legislative council in which Hong Kong's pro-democracy opposition is hoping to maintain a one-third veto bloc in the face of better mobilized and funded pro-Beijing and pro-establishment rivals.

The former British colony was handed back to China in 1997 under a "one country, two systems" agreement that promised to maintain the global financial hub's freedoms and separate laws for at least 50 years, but gave ultimate control to Beijing.

Long queues formed outside some polling stations as voters flocked to cast ballots for a record number of candidates who fanned out across the city of seven million on election day.

Much attention focused on a group of about 20 pro-democracy "localists" pushing a more radical, anti-China agenda who could become a fledgling new force in the legislature.

A growing yearning for independence and animosity towards Beijing in the southern coastal city pose one of the central government's most pressing domestic political issues.

"Hong Kong is really chaotic now. I want to do something to help," said 28-year-old Maicy Leung, who was in a snaking queue of several hundred. "It's to help the next generation and to help myself."

The stakes for Beijing are particularly high this weekend as G20 leaders gather in the eastern city of Hangzhou for a summit.

Hong Kong's opposition now controls 27 of the legislature's 70 seats, giving it a one-third veto bloc to oppose funding and various legislative bills including those it sees as eroding freedoms.

Over 50 percent of eligible voters cast ballots, with the results due early on Monday.

It will give an indication of anti-China sentiment some two years after tens of thousands took to Hong Kong streets to demand full democracy from China's Communist Party leaders.

A younger generation of activists who joined those protests is openly advocating independence - a push some people warn could jeopardize Hong Kong's economic and political future, but which seems to be gaining traction. A recent Chinese University of Hong Kong poll found around one in six people now support a separation from China.

China's stability-obsessed leaders have categorically rejected any possibility of independence.

Hong Kong officials are generally supportive of Beijing and keen to preserve "one country, two systems", though confidence in China's commitment to the formula has been shaken by recent incidents including the abduction of several Hong Kong booksellers by Chinese agents.

BEIJING CAMPAIGN

Many residents see the 79 days of student-led "Umbrella Revolution" protests in 2014 as a turning point in the city's politics even though Beijing gave no ground.

Since then, many disaffected youngsters have decried what they see as increasing Beijing interference to stifle dissent and civil liberties, leading to a radicalization of the political scene and occasional violent protests and a riot.

In July, six pro-democracy election candidates were disqualified from the election by the Hong Kong government on the grounds that they supported independence, even after some were forced to sign a pledge that Hong Kong is an "inalienable" part of China

"We don't want our next generation to be slaves of the Chinese Communist Party," said Edward Leung, one of those disqualified who campaigned for a replacement candidate in an open top bus and addressed cheering crowds of with a loudhailer.

"It's a revolution of this era," shouted Baggio Leung of Youngspiration, who was running on Leung's vacated ticket.

China has launched a multi-pronged campaign to try to sway the vote through its channels of influence including state companies and grassroots patriotic associations..

"It is an open secret that they ... pull strings, they make threats, they plant votes," said Anson Chan, a former senior Hong Kong official.

"Our election is a democratic one," Leung told reporters after casting his vote, when an activist threw a tuna fish sandwich at him. "Voters have their own free choice and don't need anyone to tell them how to vote."

(Reporting by Venus Wu, Tris Pan and James Pomfret, Editing by Robert Birsel and Angus MacSwan)